This invention relates to containers for products that tend to release gases after filling and sealing of the containers, and relates in particular to containers having a gas release vent or valve for releasing excessive gases built up within the container.
Some products, such as freshly roasted and ground coffee or yeast dough, tend to give off gases for a period of time after their preparation. For instance, when coffee that has been freshly roasted is ground, the coffee releases carbon dioxide and other gaseous substances for days or weeks. Similarly, freshly prepared yeast dough also releases carbon dioxide for a substantial period of time. In the case of ground coffee, because of the gas release, also known as off-gassing, it has customarily been the practice to store the freshly ground coffee for some time so that the majority of the off-gassing occurs before packaging the coffee, so as to avoid the sealed coffee packages being deformed or even failing as a result of the build-up of gas pressure in the packages. However, it has also been recognized that storing the ground coffee prior to packaging potentially can result in the loss of some beneficial aromatic and flavor compounds from the coffee.
Accordingly, containers have been developed that have provisions for releasing excess gas pressure from the containers so that an off-gassing product can be immediately packaged. In the case of ground coffee, this can help reduce the loss of desirable aromatic or flavor components. The prior art exhibits two basic approaches to the problem of relieving excessive gas pressure from containers for off-gassing products such as coffee or dough. One approach is exemplified by flexible coffee bags such as those described in U.S. Pat. No. 3,595,467 to Goglio, U.S. Pat. No. 5,326,176 to Domke, and U.S. Pat. No. 5,992,635 to Walters. The bags are produced from flexible web materials having gas-barrier properties. A one-way gas release valve is provided in the flexible web material. The valve allows gas to escape from the bag when the gas pressure becomes excessive, but substantially prevents air from entering the bag through the valve. Such flexible coffee bags can be prone to malfunctioning of the valve as a result of wrinkling or other deformation of the flexible material. Additionally, the bags generally are reclosable only by rolling the top of the bag down and securing the top in the rolled position using an attached wire strip or the like. Such reclosing mechanisms are inconvenient to use, and the wire strips often become detached.
The other basic approach in the prior art to the problem of relieving excessive gas pressure from containers for off-gassing products is exemplified by rigid or semi-rigid containers such as those described in U.S. Pat. No. 5,515,994 to Goglio and U.S. Pat. No. 6,733,803 to Vidkjaer. The rigid or semi-rigid containers of these patents include a flange on the upper edge of the container wall to provide a relatively large sealing surface for the attachment of a flexible membrane lid to seal the container closed. A one-way gas release valve is provided in the flexible membrane lid for relieving excessive gas pressure. Such membrane lids with gas release valves generally must be conduction heat-sealed to the flange, which is a relatively slow process. A further drawback to containers of this type arises when a replaceable overcap is included for reclosing the container after the membrane lid is removed. Because excess gas is vented through the valve in the membrane lid, the overcap or its attachment to the container must also include a provision to vent the gas, or else the overcap could prevent the valve from fulfilling its intended function. Such venting provision in the overcap may at least partially negate the resealing function of the overcap unless special steps are taken to design the venting provision in such a way that it functions to vent the released gases but does not allow air to enter the container after replacement of the overcap.
Existing one-way degassing valves are often complicated in construction and relatively expensive. The desire is to produce an effective degassing valve for a rigid package such as a thermoformed or blow-molded plastic container, at a low cost.